The invention relates to a circuit configuration for switching over a receiver circuit, in particular in DRAM memories, between a standby mode and an operating mode. A differential amplifier functions as a receiver. A control voltage derived from a reference current and serving for setting a correct operating point of the differential amplifier is generated or fed in for each differential amplifier. The invention also relates to a DRAM memory having the circuit configuration.
In the case of laptop or notebook applications, in particular, it is necessary for memory modules, in particular DRAM memory modules, which are contained therein, to also have a low current consumption in a power-down or standby mode. In the memory module, differential amplifiers function as receivers, which need a control voltage for setting the correct operating point thereof. In existing DRAM memory modules, the control voltage is generated from a reference current which is distributed through current mirrors. Whereas the receivers can be switched off in the power-down or standby mode, the distributed currents must not be switched off, in order to ensure that the receivers are immediately available again, i.e. as far as possible in one clock cycle, in the event of reactivation of the memory chip in the operating mode.
Therefore, a standby current continuously flows through the known memory chips while they are in the standby mode. The standby current is not negligible and, when a laptop or notebook is battery-operated, is a constant load on the battery. The current paths distributed through current mirrors could be switched off in the standby mode by a respective switching transistor located in the individual lines feeding the current to the receivers. However, as already mentioned above, the control voltage of the receivers must not be switched off in the standby mode, since otherwise the receivers might possibly not be able to be reactivated quickly enough in the event of switching over to the operating mode.
U.S. Pat. No. 5,557,221 (columns 1 to 16, figure sheets 1 to 8) describes and shows, in particular in FIG. 8, a circuit configuration for switching over a receiver circuit, in which switching over between a first operating mode and a second, current-saving mode is effected in a manner dependent on a frequency or amplitude present at an input.
U.S. Pat. No. 5,920,208 discloses a switch-over device for a sense amplifier with which an end of a read operation is detected through the use of a data comparison, and a switch-over to a power-down mode is performed.
It is accordingly an object of the invention to provide a circuit configuration for switching over a receiver circuit, in particular in DRAM memories, and a DRAM memory having the circuit configuration, which avoid the hereinafore-mentioned disadvantages of the heretofore-known switch-over configurations between standby or power-down mode and operating mode and which maintain a control voltage of receivers even in the standby or power-down mode with reduced standby current, in such a way that the receivers can be activated sufficiently quickly, e.g. within a few nanoseconds, in the event of a transition to the operating mode.
With the foregoing and other objects in view there is provided, in accordance with the invention, a circuit configuration for switching over a receiver circuit between a standby mode and an operating mode. The configuration comprises differential amplifiers each functioning as a receiver receiving a control voltage derived from a reference current and fed in or generated, for setting a correct operating point of the differential amplifier. A line feeds a current for generating the control voltage. Switching elements are disposed in the line for each receiver. The switching elements are permanently closed in the operating mode by an enable signal present at the switching elements for continuously supplying the current for generating the control voltage. The switching elements are closed at discrete times or periodically in the standby mode by feeding a refresh signal for discontinuously refreshing the control voltage.
Consequently, with the present circuit configuration according to the invention, the control voltage for the differential amplifiers functioning as a receiver circuit is refreshed discontinuously or periodically. In this way, the standby current for the receivers is considerably reduced. In DRAM memories, in particular, a separate generator for a periodic refresh signal for switching on the switching elements can be omitted if, as is preferred, the self-refresh signal of the DRAM memory is used. It goes without saying, however, that it is also possible to use a switch-on signal for the switching elements which is derived from the self-refresh signal and has a period that is a multiple of the self-refresh period.
In order to stabilize the control voltage fed discontinuously or periodically to the receivers, backup capacitors assigned to each receiver can be used for prolonging the refresh time.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a circuit configuration for switching over a receiver circuit, in particular in DRAM memories, and a DRAM memory having the circuit configuration, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the drawings.